192 COLOURS OF FLOWERS AS A MEANS OF ATTRACTING ANIMALS. 



surrounded below by a garland of older, rose-red flowers; and in Trifoliwm 

 spadiceum, the light-yellow centre formed by the young flowers is surrounded by 

 a zone of chestnut-brown older flowers wbereby a very remarkable colour-contrast 

 is brought about (c/. fig. 252 '). 



The contrasts met with in the umbel-like racemes of the small -flowered 

 Cruciferse are also extremely varied. These are partly produced by changes of 

 colour during the opening and fading of the flowers, partly by the increase which 

 the petals undergo very noticeably after pollination. In a group of these Cruciferae 

 of which the Whitlow-Grass, the round-fruited Penny Cress, and the Egyptian 

 Lobularia {Braba verna, Thlaspi rotvmdatum, Lobularia nummularicefolia {cf. 

 figs. 252 !■ 2' ^) may serve as types, the originally very tiny white leaves of the corolla 

 increase to twice their size, and adhere to the broad side of the ovary, which has 

 meanwhile become much enlarged, and brown or violet in colour. The ovaries, to 

 which the snow-white petals adhere, grow into young fruits, and then form a 

 wreath, just as in the species of Clover described above, around the younger white 

 flowers, as well as the central green buds. The consequence is that the whole 

 inflorescence is rendered conspicuous, although the leaves of the corolla when it 

 opens are small and insignificant. 



In a second group of the Cruciferse, of which Thlaspi alliacev/m and Thlaspi 

 arvense may be chosen as examples, the ovaries as they mature into fruits are only 

 slightly discoloured, but the green of the sepals changes in the older flowers into 

 yellow. Thus in each corymb white, yellow, and green appear side by side in a 

 varied play of colour. A third group, of which Alyssum calycinum, Draba, 

 aizoides and Arabis ccerulea, may serve as types, is rendered conspicuous by the 

 bleaching of the sepals and petals after flowering. The petals of Draba aizoides 

 and Alyssum, calycinum, which, while blossoming, were golden yellow, become 

 whitish and adhere to the young green fruits. The petals of Arabis ccerulea are 

 blue at the commencement of flowering, but fade later on and lie flat on the young 

 fruits, which have meanwhile assumed a violet tint. In these three groups of 

 Crucifers the broad side of the maturing ovary serves as a foil to the pale floral- 

 leaves, which increase in size after fading, and thus a piebald effect is given to the 

 whole inflorescence. In a fourth group, of which the Wild Cress (j^thionema) is 

 an example, the young fruits are completely enveloped by the enlarging floral- 

 leaves, and are therefore without significance as regards colour. The contrast is- 

 here obtained in the following peculiar manner: The young flowers are supported 

 side by side on short, erect pedicels at the top of a common stem, and their small, 

 expanded petals are all turned with their upper side towards the observer. After 

 fading, the pedicels lengthen, bend sideways, and project horizontally from the 

 common stalk of the whole inflorescence. The petals still grow in length and 

 breadth, and place themselves together like the leaves of a book, so that the side 

 which formerly was the lower one is now turned to the spectator. But, since the 

 upper and under sides of the petals are diff'erently coloured, the young flowers 

 crowded in the centre of the corymb exhibit a difierent colour from the old ones of 



